1. Field of the Invention
The present invention relates generally to character belt apparatus for use in line printers and more particularly, to an improved character belt apparatus having individually replaceable character slugs that are secured to and in registration with the belt.
2. Description of the Prior Art
In printers of the type used in data processing equipment, a movable endless belt supporting a plurality of type characters is moved continuously past a print line at a constant rate of speed. The type characters are equally spaced from one another and are precisely located on the belt in a single lateral track. In such printing devices, a bank of print hammers is mounted such that it can be caused to strike a selected character during the rotation of the belt in response to appropriate control signals. A print medium, such as a web of paper is fed incrementally, step by step, past the print line so as to enable the aligned bank of print hammers to appropriately impact the print. Accordingly, each hammer, when actuated, strikes the back of the paper and forces the paper against the character on the band. Because of the relative movement of the type characters on the belt and the print hammers, it will be appreciated that the character must be in precisely the expected location on the belt or misprinting will result. After a character belt has been in use for some time, wear problems have been encountered due to the continual pounding it experiences from the print hammers. It has also been observed that certain alphanumeric characters are used more frequently than others and consequently, tend to wear at a quicker rate.
One type of character belt used in date processing printers is fabricated from a fiberglass-reinforced rubber timing belt currently manufactured by the United States Rubber Company. At the upper and lower ends of each of the character slugs are rearwardly-extending undercut portions defining mutually facing ledges which are spaced apart by a distance substantially the same as the width of the belt. Accordingly, to assemble the character slugs on the belt, it is necessary to compress the belt slightly across its width, move the character slug into place and then release the belt so that the edges thereof move into the space between the rear wall portions and the front portion of the character slug. However, it is relatively expensive to fabricate this belt in view of the time required to individually assemble each character slug on the belt. Moreover, because of the resilient properties of the rubber, it was found that the location of each slug changed continuously as a function of the stretching of the belt.
Another type of character belt is formed by etching a single metal substrate and butt welding the ends together into an endless band. In fabricating this belt, a relatively thick band of metal has portions of its surface selectively etched away so as to define a set of raised characters. However, after usage it has been found that some of the more frequently-used characters wear away. Since the characters are formed integrally with the belt, the whole belt must be scrapped. Since the worn characters are not replaceable and in view of the accuracy of the etching operations that are required to form the characters, it is easily recognized that such a belt must be frequently replaced and is expensive to purchase.
Examples of printing belts are found in U.S. Pat. No. 2,928,896, entitled "High Speed Printing Devices," which issued Mar. 15, 1960, in the same name of Gerhard Dirks; U.S. Pat. No. 2,940,385, entitled "High Speed Printer," which issued June 16, 1960, in the name of Frank R. House; and U.S. Pat. No. 3,402,657, entitled "High Speed Belt Printer with Printing Slug Supporting Means," which issued Sept. 24, 1968, in the names of John T. Potter, Thomas P. Foley and Carmine J. Antonucci.